WO2004046701A2 - Appareil et procede de mesure directe in situ de coefficients d'absorption et de diffusion - Google Patents

Appareil et procede de mesure directe in situ de coefficients d'absorption et de diffusion Download PDF

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Publication number
WO2004046701A2
WO2004046701A2 PCT/US2003/036668 US0336668W WO2004046701A2 WO 2004046701 A2 WO2004046701 A2 WO 2004046701A2 US 0336668 W US0336668 W US 0336668W WO 2004046701 A2 WO2004046701 A2 WO 2004046701A2
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WO
WIPO (PCT)
Prior art keywords
diffusive
light
cavity
light intensity
attenuating
Prior art date
Application number
PCT/US2003/036668
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English (en)
Other versions
WO2004046701A3 (fr
Inventor
Edward S. Fry
George W. Kattawar
Deric J. Gray
Xianzhen Zhao
Zheng Lu
Original Assignee
The Texas A & M University System
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by The Texas A & M University System filed Critical The Texas A & M University System
Priority to AU2003290994A priority Critical patent/AU2003290994A1/en
Publication of WO2004046701A2 publication Critical patent/WO2004046701A2/fr
Publication of WO2004046701A3 publication Critical patent/WO2004046701A3/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/47—Scattering, i.e. diffuse reflection
    • G01N21/49—Scattering, i.e. diffuse reflection within a body or fluid
    • G01N21/51—Scattering, i.e. diffuse reflection within a body or fluid inside a container, e.g. in an ampoule
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/01—Arrangements or apparatus for facilitating the optical investigation
    • G01N21/03—Cuvette constructions
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/47—Scattering, i.e. diffuse reflection
    • G01N21/49—Scattering, i.e. diffuse reflection within a body or fluid
    • G01N21/53—Scattering, i.e. diffuse reflection within a body or fluid within a flowing fluid, e.g. smoke
    • G01N21/532—Scattering, i.e. diffuse reflection within a body or fluid within a flowing fluid, e.g. smoke with measurement of scattering and transmission
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2201/00—Features of devices classified in G01N21/00
    • G01N2201/06—Illumination; Optics
    • G01N2201/061—Sources
    • G01N2201/06126—Large diffuse sources
    • G01N2201/0614—Diffusing light tube with sample within
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2201/00—Features of devices classified in G01N21/00
    • G01N2201/06—Illumination; Optics
    • G01N2201/063—Illuminating optical parts
    • G01N2201/0634—Diffuse illumination

Definitions

  • This invention relates in general to measuring absorption and scattering coefficients of materials, and more particularly to an apparatus and method for direct measurement of absorption and scattering coefficients in si tu.
  • absorption coefficient can be expressed as the property of a medium that describes the amount of absorption of radiation per unit path length within the medium. It can be interpreted as the inverse of the mean free path that a photon will travel before being absorbed (if the absorption coefficient does not vary along the path) .
  • the unit quantity for an absorption coefficient is inverse length.
  • a scattering coefficient can be expressed as the property of a medium that describes the amount of scattering of radiation per unit path length for propagation in the medium.
  • the unit quantity for a scattering coefficient is inverse length.
  • an absorption coefficient describes the change in radiation intensity per unit length along the path through the medium.
  • the extinction coefficient, c is a constant that predicts the attenuation or dissipation of light at a certain wavelength.
  • light In pure water, light is highly absorbed in the infrared region of the light spectrum and poorly absorbed in the blue region. Extinction coefficients are influenced by water absorption, suspended organic and inorganic particles, and dissolved compounds.
  • the visible color in a water sample is the light that is refracted, reflected or re-emitted by substances in water because it has not been absorbed to produce heat or chemical reactions.
  • an apparatus for measuring an absorption coefficient includes a first diffusive material, a second diffusive material inside the first diffusive material separated from the first diffusive material by a cavity, and a transparent material proximate to an inner surface of the second diffusive material that holds an attenuating material.
  • First and second light detectors measure light intensities in the cavity and transparent material respectively.
  • An absorption coefficient for the attenuating material may be determined based on the first and second light intensities measured when the cavity is illuminated by a light source.
  • an apparatus for measuring a scattering coefficient includes a transparent material that holds an attenuating material, a diffusive material that substantially surrounds the transparent material, and light detectors that detect a diffused light intensity in the transparent material.
  • a light source illuminates the attenuating material with a collimated beam.
  • a scattering coefficient for the attenuating material may be determined based on the incident light intensity of the collimated beam and the diffused light intensity measured by the light detectors when the attenuating material is illuminated.
  • Important technical advantages of certain embodiments of the present invention include direct measurements of absorption and scattering coefficients. As noted above, previous techniques often require indirect measurements of absorption and scattering coefficients, such as by measurement of the extinction coefficient, that can introduce errors in real -world situations. Other such techniques involve volume integration of scattered light, which requires mathematical assumptions that may not apply perfectly to real-world situations. In contrast with such methods, certain embodiments of the present invention provide direct measurement of the scattered light intensity.
  • certain embodiments of the present invention include the use of open-ended detectors. Previous detectors required enclosed containers in order to accurately account for all of the light incident on the sample, because of the need for enclosure, introducing samples into the detector proved difficult, often requiring liquid samples to be pumped in and out of the detector. In contrast with such methods, certain embodiments of the present invention may accurately measure absorption and scattering coefficients even when the detector is open-ended, thus allowing the sample to be introduced into the container with relative ease compared to previous methods .
  • Still other technical advantages of certain embodiments of the present invention include durability under real-world use conditions. Previous enclosed detectors often included highly reflective surfaces that were prone to damage, which resulted in inaccurate measurements. Certain embodiments of the present invention protect optically sensitive components likely to be damaged by exposure to samples, thus providing a more durable detector for in si tu use.
  • FIGURE 1 is a rectangular cross-section of a cylindrical detector according to a particular embodiment of the present invention.
  • FIGURE 2 is a perspective view from one end of the detector of FIGURE 1;
  • FIGURE 3 is a flow chart illustrating one example of a method for measuring an absorption coefficient
  • FIGURE 4 is a flow chart illustrating one example of a method for measuring a scattering coefficient .
  • FIGURE 1 shows a rectangular cross section of a cylindrical detector 100 used for detecting absorption and/or scattering coefficients for an attenuating material 110 within detector 100
  • FIGURE 2 illustrates a perspective view from the end of detector 100 taken along lines 2-2 of FIGURE 1.
  • detector 100 includes an outer diffusive material 102, an inner diffusive material 104, a transparent material 106 between attenuating material 110 and inner diffusive material 104, light sources 114 and 116 for introducing light into detector 100, and detectors 118 and 120 used to measure light intensity levels at different locations in detector 100.
  • detector 100 permits the direct measurement of absorption and scattering coefficients for attenuating material 110.
  • Outer diffusive material 102 and inner diffusive material 104 comprise materials that diffuse incoming light such that the light in the medium of diffusive materials 102 and 104 is approximately isotropic. In particular embodiments in which detector 100 is substantially cylindrical, it is desirable for detector 100 to be significantly longer than its diameter in order to minimize leakage from the ends, thus increasing the accuracy of detector 100.
  • outer diffusive material 102 and inner diffusive material 104 may be formed from the highly diffusive, high- reflectance material known as SPECTRALON (cavities formed SPECTRALON are known in the art as "Spectralon cavities”) .
  • Transparent material 106 forms a tube within detector 100 that separates attenuating material 110 from inner diffusive material 104.
  • Transparent tube 106 should be substantially transparent to the wavelength of interest being measured for attenuating and scattering properties. Transparent tube 106 is in contact with diffusive material 104 allowing light to leak from inner diffusive material 104 to attenuating material 110 and vice versa. This protects the surface of inner diffusive material 104 from contact with attenuating material 110, which may increase its durability and protect inner diffusive surface 104 from damage resulting from contact with attenuating medium 110. In the depicted embodiment, transparent material 106 has a wavy inner surface that follows a generally sinusoidal curvature. The purpose for this feature will be described in greater detail below.
  • Cavity 108 between outer diffusive material 102 and inner diffusive material 104 provides a space for introduction of light into detector 100. Because cavity 108 is separated from attenuating material 110 by inner diffusive material 104, light introduced into cavity 108 will reach attenuating material 110 in a nearly isotropic manner. Accordingly, the directional effects for absorption in attenuating material 110 are diminished by the isotropy of the illumination of attenuating material
  • cavity 108 permits measurement of light intensity both as introduced into detector 100 measured in outer diffusive material 102, and after absorption by attenuating material 110, measured in inner diffusive material 104.
  • Cavity 108 may in principle be filled with any transparent material including air.
  • Attenuating material 110 represents any suitable substance to be studied that absorbs and/or scatters light.
  • Substances of interest may include water with suspended particles, plastics, tissues, fluids, or any other substance to be characterized by attenuating or scattering properties.
  • detector 100 may be used to study ocean water 110 in real world settings, such as use in ocean water by oceanographic vessels.
  • Light sources 114 represent any suitable source of illumination for cavity 108 in order to allow measure of absorption coefficients.
  • light sources 114 may be optical fibers coupled to light sources that deliver light from the sources to cavity 108.
  • light sources 114 may include wave guides, phosphorescent materials, filaments, or other suitable sources of illumination.
  • light sources 114 may be isolated from outer diffusive region 102 by a suitable coating or other barrier between light sources 114 and diffusive material 102, so that light from light source 114 does not increase the light intensity in outer diffusive material 102 other than by leakage from cavity 108. This prevents photons from light source 114 that may have directional properties from interfering with the isotropy of light in outer diffusive material 102.
  • Light source 116 introduces light into attenuating material 110 to measure scattering from attenuating material 110. It is desirable for light emitted from light source 116 to be well collimated so that the energy from light source 116 is effectively delivered into attenuating material 110. It is desirable that the light from light source 116 not impinge directly on the surface of transparent material 106. This allows the determination of the amount of scattered light to be assessed accurately based on the intensity of incoming light from light source 116 and measured intensity for the scattered light.
  • the curved inner surface of transparent material 106 facilitates scattering measurements by increasing the probability that light scattered at small angles will not be returned into attenuating material 110 by specular reflection and travel outside of the end of detector 100. This effect may also be achieved using other non-smooth surfaces for transparent material 106, such as bumpy surfaces or angular surfaces .
  • Light detectors 118 and 120 may include any suitable device for measuring intensity of light at a desired wavelength.
  • light detectors 118 and 120 are optical fibers that carry light from cavity 108 and transparent material 106 to photodetectors that measure light intensity.
  • Photodetectors may include photodiodes, photomultipliers, photoelectric detectors or any other suitable form of light detection.
  • it may be desirable to isolate light detectors 118 and 120 from particular regions of detector 100.
  • light detector 118 may be encased in an opaque covering such as aluminum foil in the region of outer diffusive material 102, cavity 108, and inner diffusive material 104 so that the measurement of light intensity is solely in transparent material 106.
  • Processor 122 comprises any suitable hardware of software for processing information.
  • processor 122 includes electronic or other types of components for receiving information from light detectors 118 and 120 and calculating absorption and scattering coefficients based on that information.
  • Processor 122 may include components for information storage (such as magnetic memory) , input devices for receiving information from detectors and/or users, output devices for displaying or otherwise generating an output of results, and any other appropriate component useful for performing tasks related to the measurement and calculation of absorption and scattering coefficients.
  • End caps 112 complete the cavities formed by inner and outer diffusive materials 102 and 104, and also hold the components of detector 100 in a fixed arrangement.
  • End caps 112 may be ring shaped and may be composed of suitable diffusive material that can be affixed to outer diffusive material 102 and inner diffusive material 104. End caps 112 may also secure transparent material 106 in place as well.
  • Components of detector 100, including end caps 112, may also be held together and/or enclosed by a housing (not shown) . Such a housing may encase the components of detector 100 to protect them from exposure to the elements and other hazards and potentially damaging influences in the environment .
  • detector 100 should be sized so as to allow adequate optical separation between inner diffusive material 102 and outer diffusive material 104; for example, the separation might be on the order of several millimeters. Furthermore, the length of detector 100 along its longitudinal axis (the direction of lines 2-2 in FIGURE 1) should be significantly longer than the transverse dimension of the sample space holding attenuating material 110 in order to avoid light leakage. As an example, for a cylindrical, meter-long detector 100, the inner diameter of transparent material 106 could be around ten millimeters. In operation, detector 100 may function in one of two modes. In the first mode, detector 100 measures the absorption coefficient of attenuating material 110. In the second mode of operation, detector 100 measures the scattering coefficient of attenuating material 110.
  • detector 100 is filled with attenuating material 110.
  • Light is introduced into cavity 108 by light sources 114. Once equilibrium light state is achieved in detector 100, the light intensity levels are measured in cavity 108 and transparent material 106 by light detectors 120 and 118, respectively. Based on these measurements, the absorption coefficient of attenuating material 110 may be appropriately determined.
  • detector 100 In the second mode of operation, light is introduced into detector 100 by light source 116. Light is scattered by attenuating material 110, passing through transparent material 106 to diffusive material 104. Diffusive material 104 diffuses scattered light so that the intensity of light in transparent material 106 represents the intensity of light scattered by attenuating material 110. This intensity is measured by light detectors 118, and the scattering coefficient may then be appropriately determined based on the amount of light introduced into detector by light source 116. Note that the measurement of light intensity in cavity 108 is not necessary to determine the scattering intensity. Accordingly, for a detector 100 that is used to measure only scattering coefficients, detector 100 may omit outer diffusive region 102, light sources 114, and detectors 120. In such a case, inner diffusive material 104 may be encased in a reflective material to prevent light from escaping or being absorbed.
  • the absorption and scattering coefficients may be determined by modeling the properties of detector 100 based on the particular materials and construction used.
  • diffusive materials 102 and 104 are Spectralon cavities
  • transparent material 106 is a quartz tube
  • attenuating material 110 is ocean water.
  • the Spectralon cavities can be modeled as an ideal Lambertian emitter and reflector, which emits equal radiance into all directions.
  • the surface albedo of the Spectralon is taken as 0.994 as an assumption, although other values can be used.
  • the index of refraction of the quartz is assumed to be 1.46.
  • the water itself has an index of refraction of 1.338.
  • a Henyey-Greenstein phase function given by
  • the cylindrical symmetry of detector 100 means that the phase function is independent of azimuthal angle ⁇ .
  • the cj-parameter is equal to the average cosine of the scattering angle ⁇ .
  • FIGURE 2 illustrates a perspective view from the end of detector 100 taken along lines 2-2 in FIGURE 1. From this perspective, the ring shape of end cap 112 is clearly visible. The inside structure of detector 100 is shown by dashed lines, which illustrate cavity 108 separating outer diffusive material 102 and inner diffusive material 104.
  • Transparent material 106 extends out from the inner surface of inner diffusive material 104 so that transparent material 106 is visible looking through the hole at the end of detector 100. Within the space enclosed by transparent material 106 is attenuating material 110. As depicted on the sides, light sources 114 and detectors 118 and 120 (hidden from this perspective by detector 118) extend into the sides of detector 100.
  • detector 100 may be enclosed in a variety of housings, and may be assembled in any suitable manner. If detector 100 does not need to be used in measuring absorption coefficient, outer diffusive medium 102 and associated components may be left out of detector 100. In the opposite case, in which scattering is not measured, specular reflection from the interface between transparent material 106 and attenuating material 110 is a much less significant concern, and accordingly, the inner surface of transparent material 106 may be made smooth.
  • detector 100 may also be used and different geometrical symmetries may be designed, although other geometries may require more complicated placements of detectors 118 and 120 and the calculations performed based on resulting measurements. These and other variations should be understood to be encompassed within the embodiments described above.
  • FIGURE 3 is a flow chart 200 illustrating a method for measuring an absorption coefficient of an attenuating material 110.
  • the first three steps of the illustrated method are calibration steps to determine the proper settings for detectors 118 and 120, in which detector 100 may be filled with a reference material having known optical properties.
  • Cavity 108 is illuminated at step 202.
  • light intensity is measured in cavity 108 and transparent material 106.
  • Detectors 118 and 120 are calibrated according to the known absorption coefficient at step 206. This step may also involve adjusting the light intensity to determine whether the scaling of the results is appropriate to enable determination of the accuracy of detectors 118 and 120.
  • Attenuating material 110 is inserted into detector 100 at step 208.
  • Cavity 108 is illuminated using light sources 114 at step 210.
  • Light intensities are measured in cavity 108 and transparent material 106 using detectors 118 and 120 at step 212.
  • absorption coefficient is determined at step 214. Steps 208 through 214 may then be repeated to perform additional measurements of the same material or other materials.
  • FIGURE 4 is a flowchart 220 that illustrates an example of a method for measuring scattering coefficient.
  • the first three steps of the illustrated method are calibration steps, in which detector 100 may be filled with a reference material with known optical properties.
  • the inside of the tube formed by transparent material 106 is illuminated at step 222 while detector 100 is filled with a reference material.
  • the light intensity in transparent material 106 is measured at step 224.
  • the light intensity produced by light source 116 may be adjusted to ensure that the proper relationship between intensity and scattering coefficient is being observed by detectors 118. Based on those measurements, detectors are calibrated at step 226.
  • Attenuating material 110 is introduced into detector at step 228. Attenuating material 110 is illuminated using light source 116 at step 230. Light intensity in transparent material 106 is measured using detectors 118 at step 232. The incoming light intensity from light source 116 is determined at step 234. This light intensity may be known from the properties of light source 116, or may be measured using photodetectors or other suitable techniques. Based on the measured light intensity in transparent material 106 and the light intensity incident on attenuating material 110, the scattering coefficient may be determined at step 236. Steps 228 through 236 may then be repeated to perform measurements on the same material or different materials.

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  • Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Investigating Or Analysing Materials By Optical Means (AREA)

Abstract

La présente invention concerne un appareil permettant de mesurer un coefficient d'absorption et comportant un premier matériau diffusible, un second matériau diffusible situé à l'intérieur du premier matériau diffusible et séparé du premier matériau diffusible par une cavité, et un matériau transparent situé à proximité d'une surface interne du second matériau diffusible qui contient un matériau d'atténuation. Un premier et un second détecteur de lumière mesurent les intensités lumineuses dans la cavité et dans le matériau transparent respectivement. Un coefficient d'absorption pour le matériau d'atténuation peut être déterminé sur la base de la première et de la seconde intensité lumineuse mesurée lorsque la cavité est éclairée par une source de lumière.
PCT/US2003/036668 2002-11-15 2003-11-17 Appareil et procede de mesure directe in situ de coefficients d'absorption et de diffusion WO2004046701A2 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2003290994A AU2003290994A1 (en) 2002-11-15 2003-11-17 Apparatus and method for direct measurement of absorption and scattering coefficients in situ

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US42673302P 2002-11-15 2002-11-15
US60/426,733 2002-11-15

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WO2004046701A3 WO2004046701A3 (fr) 2004-06-24

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ES2645527T3 (es) * 2005-10-10 2017-12-05 FAUDI Aviation GmbH Sonda, sensor y método de medición
US7544234B2 (en) * 2006-01-26 2009-06-09 Bendix Commercial Vehicle Systems Llc Vehicle air system having an indicator device and method
WO2012020440A1 (fr) 2010-08-12 2012-02-16 Consiglio Nazionale Delle Ricerche Dispositif pour spectroscopie en lumière diffuse
DE102016116100A1 (de) 2016-08-30 2018-03-01 B. Braun Avitum Ag Erfassungsvorrichtung für ein Medium in einem Schlauchabschnitt
EP3526560A4 (fr) * 2016-10-11 2020-07-08 Victoria Link Limited Appareil spectromètre permettant de mesurer des spectres d'un échantillon liquide à l'aide d'une cavité d'intégration

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US5424840A (en) * 1992-07-21 1995-06-13 The State Of Oregon Acting By And Through The State Board Of Higher Education On Behalf Of Oregon State University In situ chlorophyl absorption meter
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US5424840A (en) * 1992-07-21 1995-06-13 The State Of Oregon Acting By And Through The State Board Of Higher Education On Behalf Of Oregon State University In situ chlorophyl absorption meter
US5712710A (en) * 1996-10-15 1998-01-27 Cetin Karakus Spectrophotometric probe for insitu measurement
DE19751403A1 (de) * 1996-11-15 1999-05-20 Optosens Optische Spektroskopi Kombinierte Absorptions- und Reflektanzspektroskopie zur synchronen Ermittlung der Absorption, Fluoreszenz, Streuung und Brechung von Flüssigkeiten, Gasen und Festkörpern

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US7057730B2 (en) 2006-06-06
WO2004046701A3 (fr) 2004-06-24
US20040141179A1 (en) 2004-07-22
USRE41682E1 (en) 2010-09-14
AU2003290994A1 (en) 2004-06-15

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